The federal Centers for Disease Control and Prevention (CDC) says homosexual men accounted for 65 percent of the nearly 12,000 cases of syphilis in the United States in 2007, making them the “primary driver” of increased syphilis rates overall.

In a report on sexually transmitted diseases (STDs) issued Tuesday, the government said syphilis, a disease that was almost eliminated as a public health threat less than 10 years ago, is on the rise -- with cases increasing each year since 2000.

It remained a serious health threat in the United States in 2007, the latest year for which statistics are available, largely because of increased transmission among “men who have sex with men” (MSM) in the United States, according to the CDC.

Dr. Gary Rose, president of the Texas-based Medical Institute for Sexual Health, told CNSNews.com that there are several factors behind the rise.

“One of the problems for men who have sex with men is that their sexual encounters are frequently anonymous,” Rose said. “The more partners you have, the higher the risk of transmission for any sexually transmitted infections.”

Rose said the government has spent a lot of time and money promoting condoms among men who have sex with men.

“Condoms are 85 percent effective against HIV in vaginal intercourse,” he said, “but there really have been no good studies on their use in anal intercourse.”

But even among heterosexuals when condoms are used 100 percent of the time, the amount of risk-reduction is only 50 percent.

Chlamydia, meanwhile, is at an all-time high, increasing nearly 7 percent since 2006, the report said.

Rose said one thing that most people don’t understand is that gonnorhea, syphilis and Chlamydia can be transmitted through oral sex.

“That is, of course, a problem, not only for men having sex with men, but it is also an increasing problem for young people – especially black teens.”

African-Americans, who make up 12 percent of the U.S. population, accounted for almost 50 percent of syphilis and chlamydia cases (48 percent and 46 percent respectively) – and a whopping 70 percent of reported cases of gonorrhea in 2007,

CDC reported.

Young black women, 15- to 19-years-old, had the highest rates for both chlamydia (9,647 cases per 100,000 population) and gonorrhea (2,956 cases per 100,000 population) of any group.

The racial disparities in STD rates are among the worst health disparities in the nation for any health condition, according to Dr. John M. Douglas Jr., director of the CDC's division of STD preventione.

"We must intensify efforts to reach these communities with needed screening and treatment services,” Douglas said. “Testing and the knowledge of infection is a critical first step toward reducing the continued consequences of these diseases."

Knowledge is especially key to fighting Human Papillomavirus, or HPV. – a major concern of health educations, Rose said.

“The number of cases of head and neck cancer are rising significantly, because HPV attacks the tissues of the head and neck in the same way it attacks the cervix,” Rose told CNSNews.com.

HPV is a major cause of cervical cancer among women – and a woman can unknowingly have the virus for years before tumors are triggered.

CDC estimates that almost 19 million new sexually transmitted infections occur each year – with almost half of those among 15- to 24-year-olds. STDs cost the U.S. health care system as much as $15.3 billion annually.